1. Field of the Invention
This invention relates to an incubator which is used in a biochemical analysis system, in which a sample such as blood or urine is spotted onto a dry analysis element and, for instance, the concentration of a specific biochemical component contained in the sample is detected, to keep the dry analysis element at a constant temperature in order to measure change of the optical density.
2. Description of the Related Art
Recently, there has been put into practice a colorimetric dry (dry-to-the touch) analysis element with which the content of a specific biochemical component or a specific solid component contained in a sample liquid can be quantitatively analyzed by simply spotting a droplet of the sample liquid. Since being capable of analyzing samples easily and quickly, the biochemical analysis systems using such dry analysis elements are suitably used in medical institutions, laboratories and the like.
When quantitatively analyzing the chemical components or the like contained in a sample liquid using such a colorimetric dry analysis element, a droplet of the sample liquid is spotted on the analysis element, and the analysis element is held at a constant temperature for a predetermined time in an incubator so that a coloring reaction (pigment forming reaction) occurs, and the optical density of the color formed by the coloring reaction is optically measured. That is, measuring light containing a wavelength which is pre-selected according to the combination of the component to be analyzed and the reagent contained in the analysis element is projected onto the analysis element and the optical density of the analysis element is measured. Then the concentration of the component to be analyzed is determined on the basis of the optical density according to a calibration curve representing the relation between the concentration of the specific biochemical component and the optical density.
When the distance between the dry analysis element and the light measuring head (a head for projecting said measuring light onto the dry analysis element and receives light from the dry analysis element bearing thereon the optical density of the dry analysis element fluctuates, there can be produced measuring errors since the light measuring head has own optimal measuring distance due to its light measuring sensitivity properties as will be described later in conjunction with FIG. 4. In order to accurately measure the concentration of a specific component in the sample, it is necessary to detect even a slight coloring reaction and it is required for the colorimetry to be carried out at a high accuracy. Accordingly, it is important to keep constant the distance between the dry analysis element and the light measuring head.
In Japanese Patent Publication No. 5(1993)-72976, the optical components of the light measuring head are positioned where the output of the light measuring head is maximized, so that the influence of variation of the distance on the light measuring sensitivity is minimized.
In U.S. Pat. No. 5,037,613, there is disclosed a structure in which the lower surface of the outer periphery of the incubator rotor, which is rotated with dry analysis elements spotted with the samples accommodated therein, is supported by a sliding support so that the rotational displacement of the incubator rotor is suppressed and the distance between the light measuring head and each of the dry analysis elements arranged along the outer periphery of the incubator rotor is held constant.
However, the approach disclosed in the aforesaid Japanese patent publication is disadvantageous in that though fluctuation of the distance can be held in an acceptable range where the influence of variation of the distance on the light measuring sensitivity can be suppressed by the arrangement of the optical components so long as the diameter of the incubator rotor is small and the rotational displacement of the incubator rotor is small, fluctuation of the distance becomes too large for the optical components to suppress the influence of variation of the distance on the light measuring sensitivity in an acceptable range when the number of the dry analysis elements to be accommodated in the incubator increases and the diameter of the incubator rotor increases. An attempt to limit the rotational displacement of a large incubator rotor increases requirement on processing accuracy and fabricating accuracy of the components of the incubator rotor, thereby adding to the manufacturing cost of the incubator.
The approach disclosed in the United states patent is disadvantageous in that as the sliding support wears, the rotational displacement of the incubator rotor increases and the incubator rotor drive mechanism can become unstable due to nonuniform load and wear of the sliding support will produce dust.
Displacement in height of the incubator rotor relative to the measuring head during rotation of the incubator rotor is generated by strain generated when forming the rotor and/or strain generated when mounting the rotor on the rotating shaft. Accordingly, the distance between the measuring head and each of the element chambers arranged along the outer periphery of the incubator rotor when the element chamber is brought to a predetermined position, e.g., a light measuring position where the optical density of the dry analysis element is to be measured, is constant for each element chamber but differs from chamber to chamber. As the difference in the distance between the measuring head and the element chambers increases, variation in the measured value for a given optical density becomes larger.
As disclosed, for instance, in Japanese Unexamined Patent Publication No. 11(1999)-237386, there has been known an incubator provided at its center with an element discarding hole through which dry analysis elements after measurement are discarded by pushing the dry analysis elements further inward by the element transfer member which pushes the dry analysis elements into the element chambers of the incubator. This structure is advantageous in that the dry analysis elements can be easily discarded with the transfer mechanism of a simple structure.
However, as the number of the dry analysis elements to be accommodated in the incubator increases and the diameter of the incubator rotor increases, the diameter of the discarding hole must be large in order to discard the dry analysis elements in all the element chambers by a limited stroke of the element transfer member. When the diameter of the discarding hole is enlarged and the diameter of the rotating shaft of the incubator rotor is increased, the diameter of the bearing member for supporting the rotating shaft must be large, which adds to the manufacturing cost of the bearing member. Especially when the bearing member must support the rotating shaft of the incubator rotor so as to suppress the rotational displacement of the incubator rotor in the acceptable range as described above, the manufacturing cost of the bearing member is further increased.
On the other hand, when the diameter of the element discarding hole is reduced, the distance over which the dry analysis elements are conveyed to be discarded becomes longer, which adds to the length and stroke of the element transfer member and increases the overall size and weight of the apparatus.